Electrospray is a liquid atomization method that may be utilized for a wide range of applications, from being used as an ionization source for mass spectrometry to generating nanometer sized droplets, or fibers in nanotechnology.
The electrospray emitter or nozzle may be a simple metallic capillary that may have a blunt tip. A liquid (i.e., electrospray medium) may be pumped with a flow rate of Q through the capillary, and a high voltage of V may be applied to the capillary. The capillary tip may be situated at a distance from a grounded electrode and the application of the voltage V between the capillary and the grounded electrode may lead to formation of an electrical field between the capillary tip and the grounded electrode. As the liquid leaves the tip of the capillary it may form a meniscus at the capillary tip. The meniscus may then deform into a conical shape under the electrical field. The conical shape is referred to as Taylor cone, from which a fine jet may erupt and subsequently this jet may break up either into fine droplets (i.e., electrospray) or extracted as fine fibers (i.e., electrospinning). This mode of operation, in which a Taylor cone and a jet is formed, may be referred to as a cone-jet mode.
An ideal electrospray emitter should allow for formation of a stable Taylor cone in order to ensure a robust operation of the electrospray system in a cone-jet mode. The emitter should allow for formation of a stable cone-jet for a large range of flow rates Q and voltages V. The ranges of Q and V in a Q-V space, for which a stable cone-jet may be formed, may be referred to as a stability margin or stability envelope for an electrospray system.
There is, therefore, a need in the art for an electrospray system with an emitter having a large stability margin. There is further a need in the art for an electrospray system capable of having a stable operation, i.e., the Taylor cone that may form in the operation will not frequently change its height, or detach from the jet under various external disturbances, such as small mechanical vibrations of the emitter, or fluctuations in ambient gas flow around the emitter or in the flow rate Q.